A and C are both correct. Letter A uses the present subjunctive and letter C uses the past subjunctive. It really is a matter of choice in English. Here are two examples:
"It's time I be made a partner."
"It's time I were made a partner."
Both of these mean the same thing. I know your ESL teacher wants the past subjunctive "left" used above and not the present subjunctive "leave", so he might frown on my first example; however, both are correct in my examples and both A and C are correct in your situation, whether your ESL teacher "believe" it or not (present subjunctive). There are a few times in English wherein the present and past subjunctive forms can be used interchangeably; this is one of them. The second example using "were" or your example using "left" may give off a hint that it is more unlikely to happen than it would be if the present subjunctive were used therein, but it really is preference.
Other examples of present and past subjunctive interchangeability:
"I would rather he be in agreement."
"I would rather he were in agreement."